A dietary supplement containing the antioxidants beta carotene and vitamins C and E, as well as the mineral magnesium, reduced the likelihood of hearing loss in guinea pigs taking the antibiotic gentamicin. (Credit: Mariposa Veterinary/Flickr)

A dietary supplement may offer protection against hearing loss that sometimes occurs after taking antibiotics, according to research with guinea pigs.

Estimates indicate that up to 25 percent of people who take a class of antibiotics called aminoglycosides experience hearing loss. Aminoglycosides are used to treat infections that are resistant to other antibiotics, including penicillin or amoxicillin.

[related]

“In developing countries aminoglycosides are often used as a first-line treatment for any infection because they are so cheap and so readily available,” says Colleen Le Prell, associate professor in the department of speech, language, and hearing sciences at the University of Florida.

Researchers tested the use of a dietary supplement containing the antioxidants beta carotene and vitamins C and E, as well as the mineral magnesium, for protection against hearing loss caused by the antibiotic gentamicin.

Hearing loss is largely caused by the production of free radicals, which destroy healthy inner ear cells. The antioxidant vitamins prevent hearing damage by “scavenging” the free radicals and protecting against their effects.

In previous studies, Le Prell demonstrated that these supplements prevented noise-induced hearing loss in animals. She is currently testing the vitamin combination in human clinical trials.

“We’re enthusiastic about the use of these vitamins because of the significant safety profile that exists,” Le Prell says. “These agents are generally regarded as safe with very well-known recommended daily intakes.”

Guinea pigs

Before and during administration of the antibiotic, half the animals ate traditional chow and the other half received food enriched with the vitamin supplements. Scientists tested the guinea pigs’ hearing before and up to nine weeks after antibiotic treatment by measuring the animals’ brain stem activity in response to brief sound bursts.

The researchers found that animals that received the dietary supplement had better maintenance of hearing than animals that ate the standard diet.

“The best protection was obtained at lower test frequencies and that’s important because the lower frequencies are essential for speech,” Le Prell says.

40 decibels of hearing

Researchers also examined the inner and outer hair cells in the animals’ ears. In humans, death of outer hair cells results in a loss of about 40 decibels of hearing, so these cells are critical for normal hearing, Le Prell says.

While some of the animals in the control group experienced complete outer hair cell death after receiving gentamicin, those animals that had the vitamin-enriched diet fared much better.

Future research should examine whether combining aminoglycosides with the vitamin mix can cause a drug interaction that may affect the antibiotics’ efficacy.

A preliminary study shows that gentamicin’s effectiveness wasn’t lowered by the vitamins, but more research is needed before moving to clinical trials, Le Prell says.

“The long-term vision is clearly to see whether you can get the same benefit in human patients who are being treated with these aminoglycosides.”

Josef Miller of the University of Michigan is a co-author on the study, which was supported in part by a grant from the National Institute on Deafness and Other Communicative Disorders.